Intel Extensible Firmware Interface User Manual
Page 304
Extensible Firmware Interface Specification
10-10
12/01/02
Version 1.10
Description
The
SIMPLE_TEXT_OUTPUT
protocol is used to control text-based output devices. It is the
minimum required protocol for any handle supplied as the
ConsoleOut
or
StandardError
device. In addition, the minimum supported text mode of such devices is at least 80 x 25
characters.
A video device that only supports graphics mode is required to emulate text mode functionality.
Output strings themselves are not allowed to contain any control codes other than those defined in
Table 10-1. Positional cursor placement is done only via the
function.
It is highly recommended that text output to the
StandardError
device be limited to sequential
string outputs. (That is, it is not recommended to use
SetCursorPosition()
on output messages to
StandardError
.)
If the output device is not in a valid text mode at the time of the
call, the
device is to indicate that its
CurrentMode
is –1. On connecting to the output device the caller is
required to verify the mode of the output device, and if it is not acceptable to set it to something it
can use.